Coolie labour was for centuries the dirty little non-secret of the British Empire, and a few years ago, a calamity here showed that, in 21st-century Britain, it is alive and well. In February 2004, 23 illegal Chinese immigrants were drowned in Morecambe Bay, trapped by the terrifyingly fast incoming tide while picking cockles. Three Chinese gangmasters were imprisoned, but none of the English client-base was ever held to account. The 58 Chinese immigrants found dead in a lorry in Dover three years earlier was horrifying enough, but this was a grotesque mass death nurtured well within our national boundaries, cultivated by UK market forces in the heart of picturesque seaside England.

It is this shameful episode that is dramatised by documentary film-maker Nick Broomfield in a rare fiction feature. It is a gruelling journey comparable to Michael Winterbottom's In This World, undertaken in the company of an illegal called Ai Qin from the Fujian province of China, played by first-timer Ai Qin Lin. Her fellow serfs are played by former Chinese illegal immigrants, on whose testimonies Broomfield has based his script, including, presumably, the scenes showing British employment agencies greedily expecting "presents" from gangmasters.

Broomfield begins and ends his movie on the Morecambe beach: not a haven for holidaymakers, but a huge, empty, cruel space which looks like something from the end of the universe. It seems like Ai Qin and her wretched friends have been finally washed up on some vast shore in a netherworld of undreamt-of callousness and indifference. The "ghosts" of the title refers to how Chinese refer to the Anglo-Saxons, but the word is more comparable to the illegals themselves, dead in spirit, drifting unacknowledged through the UK's service industry.

The movie shows a new, alien, exotically grim England - the England that the illegals see. Ai Qin awakes in her overcrowded, rented, two-bed house in a gaunt housing estate to look on to a cheerless landscape into which globalisation has transplanted the chill of world poverty. Broomfield avoids the metropolitan cliches of neon-lit Chinatown with its seedy glamour and takes us instead to Thetford in Norfolk and then to Morecambe, places the English complacently assume to be homes of provincial decency. Instead, they look like new centres of hypocrisy, brutality and racism.

At first, Ai Qin works back-breakingly hard picking spring onions: her master informs her curtly these wares are for Sainsbury, Asda and Tesco - the unfamiliar names invoked like those of the sternest local chieftains. Later, Ai Qin has the mortifying experience of shopping in a local supermarket and realising that she cannot afford a bunch of the spring onions that she had just that morning held in her hands, as plentiful as weeds. Then she is moved up north for even harsher, harder work. Her final nightmare in Morecambe is unwatchably grim, and surely very dangerous to film. The one unreality, it seems to me, is that the workers' terrified faces are lit. In reality, the tragedy must have unfolded in pitch darkness.

This is a strong foray into features for Nick Broomfield, though it is maybe unusual to have a Broomfield film without his trademark voiceover - to get the drama straight, and not filtered through the director's unmistakable quizzical lilt. He may not yet have the well-worked idiom of a Ken Loach, nor does this film, with its austere and perhaps stolidly paced narrative, have the coiled dramatic power of films like the Dardennes brothers' The Child or Lukas Moodysson's Lilya 4-Ever. But it's a valuably tactless, steady, clear-eyed look at the tragedy and cruelty of the new globalised serfdom.